Although adolescents represent less than 0.5% of all the reported cases of AIDS in the United States, the impact of HIV infection on the health and well-being of adolescents is much larger than these figures might imply. Unfortunately, to date many of the important questions concerning HIV infection in adolescents have neither been asked nor answered. Via a prospective, longitudinal study of HIV infected and non-infected adolescents, this study seeks to investigate the full spectrum of HIV infection in adolescents. Medical, biobehavioral, psychosocial, as well as access and utilization questions will be addressed concerning these underserved patients. The study cohort will be recruited from multiple clinical sites throughout the United States. These sites will be brought together under the umbrella of a national network of multiple clinical and basic science programs. Approximately 200 HIV infected adolescents will be enrolled into a standardized base protocol to characterize the population based spectrum of disease, disease progression and the effect of other sexually transmitted diseases and pregnancy on HIV infection. Once the base protocol is in place, special studies will be undertaken to address a number of unresolved questions including issues of susceptibility, infectivity, and transmissibility of HIV infection in adolescents. The network will also work with member units to establish a clinical research interface to ensure access to clinical drug and vaccine trials.